The corrosion of lead anodes in copper electrowinning
- PDF / 495,664 Bytes
- 5 Pages / 612 x 783.28 pts Page_size
- 1 Downloads / 219 Views
T I - I O U G H a wide v a r i e t y of anode m a t e r i a l s h a s b e e n u s e d in the e l e c t r o - w i n n i n g of c o p p e r , l e a d a l l o y s have b e c o m e s t a n d a r d anode m a t e r i a l b e c a u s e of t h e i r l o w c o s t . In the e l e c t r o w i n n i n g of c o p p e r f r o m s u l f u r i c a c i d l e a c h s o l u t i o n s and f o r the d e c o p p e r i z a t i o n of r e f i n e r y e l e c t r o l y t e , a n o d e s c o m p o s e d of c o m m e r c i a l l y p u r e (CP) l e a d o r , m o r e f r e q u e n t l y , l e a d h a r d e n e d with up to 12 p c t a n t i m o n y a r e often used. While t h e s e a l l o y s a r e c o n s i d e r e d a d e q u a t e in m a n y a p p l i c a t i o n s , in o t h e r i n s t a n c e s s e r i o u s c o r r o s i o n o c c u r s which is c o s t l y in t e r m s of f r e q u e n t anode r e p l a c e m e n t and in c o n t a m i n a t i o n of the c a t h o d e s with the l e a d f r o m the corroded anodes. For example, CP lead anodes were found to c o r r o d e r a p i d l y at C h u q u i c a m a t a , Chile owing to the p r e s e n c e of s m a l l a m o u n t s of HNOz and HC1 in the c o p p e r l e a c h e l e c t r o l y t e . Fink and E l d r i d g e 1 t e s t e d l e a d d o p e d with s e v e r a l e l e m e n t s in v a r i o u s c o m b i n a t i o n s in o r d e r to d e c r e a s e t h i s c o r r o s i o n . T h e s e a u t h o r s s t a t e d that C P l e a d a n o d e s w e r e a d e q u a t e in s t r a i g h t s u l f a t e s o l u t i o n s . Koenig et al 2 s t u d i e d the effect of t r a c e a m o u n t s of v a r i o u s c a t i o n s (Co, F e , Mn, Ni, C r , Na and Mg) in the e l e c t r o l y t e on the a m o u n t of l e a d c a r r i e d f r o m the anode to the cathode in e l e c t r o w i n n i n g z i n c . T h e y a l s o a l l o y e d Pb with Sb, Ag and o t h e r m e t a l s to r e d u c e l e a d c o n t a m i n a t i o n . Schlatn and c o w o r k e r s s t e s t e d v a r i o u s a l l o y s of l e a d f o r c o r r o s i o n r e s i s t a n c e in the e l e c t r o w i n n i n g of m a n ganese. More recently solvent extraction has been developed to c o n c e n t r a t e and p u r i f y c o p p e r s o l u t i o n s p r i o r to e l e c t r o w i n n i n g . While t h i s h a s i m p r o v e d e l e c t r o w i n ning c u r r e n t e f f i c i e n c i e s and c a t h o d e quality, it h a s m a r k e d l y i n c r e a s e d the c o r r o s i o n of the a n t i m o n i a l lead anodes employed. This accelerated corrosion h a s f r e q u e n t l y b e e n a t t r i b u t e d to the high a c i d l e v e l s (up to 300 g / l ) e n c o u n t e r e d in t h e s e s o l u t i o n s . Although e q u a l l y high HzSO4 l e v e l ~ a r e e n c o u n t e r e d in d e c o p p e r i z a t i o n c i r c u i t s in e l e c t r o l y t i c r e f i n e r i e s , the anode c o r r o s i o n r a t e s have not b e e n a s high a s t h o s e in s o l vent e x t r a c t i o n - e l e c t r o w t n c i r c u i t s .
Data Loading...
